Is universe expanding or contracting?

In summary: There was no point. In summary, the universe is expanding and gravity is pulling two galaxies closer to each other.
  • #1
utkarsh009
47
0
gravity pulls two galaxies. Andromeda and Milky Way are going to collide in few billion years. this seems to show that everything in the universe is moving close to each other i.e. contracting. but, since the universe was formed, it has been expanding due to dark energy. how do you explain this? secondly, are they (force by dark energy and gravity) in equlibrium? if not which one is dominating?
 
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  • #2
The universe is definitely expanding. However, the expansion is only dominant on large scales. At small scales, gravity wins out, and that is why Andromeda and the Milky Way are getting closer together. Think about it this way... if I drop a ball, it falls to the group due to the Earth's gravity. Does that mean the universe isn't expanding?

but, since the universe was formed, it has been expanding due to dark energy.
This is a false statement. First, dark energy was essentially negligible in the early stages of the universe. Second, even if there was no dark energy, the universe would still be expanding. The effect of dark energy is to cause the universe to expand at an accelerating rate.

secondly, are they (force by dark energy and gravity) in equlibrium? if not which one is dominating?

Well the universe continues to expand at an accelerating rate, so you could say that dark energy is dominating.
 
  • #3
Thank you nicksauce. it was a very well written answer. i also discovered a new fact in the process. (the one that was false).
 
  • #4
utkarsh009 said:
gravity pulls two galaxies. Andromeda and Milky Way are going to collide in few billion years. this seems to show that everything in the universe is moving close to each other i.e. contracting. but, since the universe was formed, it has been expanding due to dark energy. how do you explain this? secondly, are they (force by dark energy and gravity) in equlibrium? if not which one is dominating?

That depends on your POV. From inside it looks expanding, from outside it looks contracting.
 
  • #5
robheus said:
That depends on your POV. From inside it looks expanding, from outside it looks contracting.

:confused: What does this mean?
 
  • #6
George Jones said:
:confused: What does this mean?

Don't bother.

Actually I was waiting for some clever response like "there is no outside to the universe".
 
  • #7
robheus said:
Don't bother.

Actually I was waiting for some clever response like "there is no outside to the universe".
Ok...so what is the point then?
 
  • #8
russ_watters said:
Ok...so what is the point then?

There was no point.
 

1. Is the universe expanding or contracting?

According to current scientific understanding, the universe is expanding. This means that galaxies, stars, and other objects within the universe are moving away from each other at an accelerating rate.

2. How do we know that the universe is expanding?

Scientists have observed the redshift of light from distant galaxies, which indicates that they are moving away from us. This redshift is caused by the stretching of space as the universe expands. Additionally, the cosmic microwave background radiation, leftover from the Big Bang, also supports the idea of an expanding universe.

3. Will the universe continue to expand forever?

It is currently believed that the universe will continue to expand indefinitely. However, there are some theories that suggest the expansion may eventually slow down or even reverse, leading to a contraction of the universe.

4. How fast is the universe expanding?

The rate of expansion, known as the Hubble Constant, is approximately 70 km/s per megaparsec. This means that for every 3.3 million light years, the universe is expanding by 70 kilometers per second.

5. Is the expansion of the universe uniform?

No, the expansion of the universe is not uniform. The rate of expansion can vary in different parts of the universe, and the expansion is also affected by the presence of matter and energy. This can result in some areas of the universe expanding faster or slower than others.

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